Balaenoptera acutorostrata [Common Minke Whale]
× Balaenoptera bonaerensis (♀) [Antarctic Minke Whale] NHR. These whales normally have disjunct ranges, but genetic analyses have confirmed that a female Antarctic minke whale that made an unusual migration to Arctic waters did in fact produce a hybrid with a common minke whale. This was the first documented case of such migration between the two hemispheres and of hybridization between these two whales. Glover 2010.

Balaenoptera musculus [Blue Whale]
× Balaenoptera physalus (↔) [Fin Whale] ONHR. These whales occur in mixed schools. CON: All oceans (hybrids have been reported from both the northern Atlantic and northern Pacific). HPF(♀♀). In the latter half of the twentieth century only five hybrids, three female and two male, have been reported. Three were caught off Iceland during the 1980s and their hybridity was confirmed by molecular analysis. One was pregnant (after backcrossing with a blue whale). Spilliaert et al. (p. 188) thought the presence of a corpus albicans in this individual indicated a prior pregnancy. Another hybrid was killed off the coast of Spain in 1984. Doroshenko reported a hybrid captured in 1965 off Kodiak Island (Gulf of Alaska). However, such hybrids have long been known and were far more common formerly, when blue and fin whales were themselves more abundant. In Norwegian waters alone, Cocks (1887) lists (pp. 217-218) ten such hybrids captured in the single year of 1886, and says (p. 216) that they were well-known to the whalers: "Nearly universally recognised among the Finwhalers is the so called "Bastard," from its having been supposed to be the offspring of mixed parentage—of a Blue and Common Rorqual. This variety appears to attain to larger dimensions than the typical form, and is described as grey, rather than the usual white, on the under side; on one side the baleen plates are for a short distance at the anterior end entirely white, while the remaining portions are darker than the normal colour." He further says that the hybrids are larger on average than either the fin or blue whale (which would make these hybrids the largest animals on earth). One reached "the remarkable length of 80 1/2 Eng. ft. This Whale was shot by the ‘Murmanetz’ on April 9th, the harpoon going well in just behind a flipper, that is, somewhere very close to the heart, and the shell exploded. The wound, instead of proving almost immediately fatal, seemed to madden the victim, and it rushed away at great speed and towed the steamer, with the propeller working full speed astern, for four hours when the 'Welda' being sighted, she was signalled to assist, and this vessel, steaming up at an angle, succeeded in lodging a harpoon just behind the flipper on the opposite side to the first; this shell also exploded properly. The Whale in this mortally wounded condition actually towed the two steamers steaming full speed astern, with a boat from each constantly lancing it, for two hours before it succumbed" (Cocks 1887, p. 217). Two of the female hybrids listed by Cocks (see pp. 217 and 218) were pregnant. Árnason 1995; Árnason and Gullberg 1993; Árnason et al. 1991; Spilliaert et al. 1991; Bérubé and Aguilar 1998†; Doroshenko 1970.
× Megaptera novaeangliae (♂) [Humpback Whale] NHR. CON: Oceans worldwide. Folkens et al. (2002, pp. 236-237) say that "unlikely as it would seem given the considerable differences in size and morphology between the two species, there is one well-documented report of a Humpback-Blue Whale hybrid from the South Pacific." Blue whales (~30 m) are nearly twice as long as humpbacks (~17 m), and far heavier (maximum weight 180,000 kg vs. ~40,000 kg). Internet reports say the mother was a blue whale.